The present invention relates generally to hand held power tools.
Hand power tools are known and widely utilized. In order to avoid uncontrollable rotation of a hammer drill which is held by a user during blocking a drill or a drill crown in a masonry, it is known to connect the drill or the drilling crown with a drive of the hammer drill through a safety coupling. The safety coupling opens when the drill is blocked.
German patent document DE 38 32 202 C1 discloses a hand power tool with such a safety coupling. The safety coupling for transmission of torque has a first radially inner coupling part and a second coupling part which surrounds the first coupling part. The coupling parts are connected with one another through arresting elements which are formed as rollers. The rollers are guided in a first coupling part in guiding passages. Springs are arranged in the guiding passages and are supported at their first ends against a passage bottom. With their second ends, they act radially outwardly on the rollers in direction to the second coupling part and press the rollers into the recesses of the second coupling part. When a predetermined torque is exceeded, the rollers are pressed radially inwardly from the recesses against the springs and open the safety coupling. The rollers slide subsequently over the recesses.
Accordingly, it is an object of present invention to provide a hand power tool which is a further improvement of the existing hand power tools.
More particularly, it is an object of the present invention to provide a hand power tool with at least one safety coupling in a drive train which for transmission a torque around a rotary axis has at least two coupling elements connected with one another through an arresting element loaded by a spring and held in a guiding passage, which interrupts arresting in response to exceeding of a predetermined torque.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a hand power tool of the above mentioned type, in which the spring is supported in direction of the arresting element through a guiding element, which is non rotatably guided through guiding surfaces in the guiding passage at least around an axis extending parallel to the rotary axis.
A bending moment transmitted from the arresting element to the spring, a buckling of the spring, a contact of the spring with a passage wall and thereby loading and a spring breakage can be avoided, and a long service life can be obtained, in particular for fast rotating hand power tools.
The guiding passages can be produced by various methods and can have various cross-sections, for example round, ellipsoidal or conical cross-sections. The guiding passages can be for example drilled or sintered, and the guiding passages which are sintered can be formed for example with corners.
The spring can be supported in direction of the arresting element through various supporting surfaces which are shaped in a known manner, for example through a curved, concave and/or convex supporting surfaces. A tilting moment caused by the supporting surface can be avoided in a structurally simple and cost favorable manner by a flat supporting surface, whose normal line extends parallel to an actuating direction of the guiding element in the guiding passage.
In accordance with a further embodiment of the present invention, the spring at its end which faces the guiding element and/or at its end which faces away from the guiding element, is guided through a short recess and/or a short projection. The spring can be exactly positioned during mounting, and then during operation held in its position. The spring over its whole length can operate free without guidance. The guiding passage can be formed with a sufficient distance from the spring with its side walls, in the case of open safety coupling, or in other words with compressed spring. A contact between the side walls of the guiding passage and the spring, as well as friction and wear can be avoided, and a long service life can be provided.
In accordance with a further embodiment of the present invention, it is further proposed that the spring is oriented parallel to the side walls of the guiding passage. An equal distance between the spring and the side walls can be provided over the length of the spring, and in space economical manner, a contact between the spring and the side walls can be avoided.
When the elastic element is formed as a component which is rotatable around an axis extending parallel to the rotary axis, the friction and wear between the arresting element and the corresponding coupling element is reduced by a rolling movement. For saving additional components, mounting expenses and costs, the arresting element or the guiding element can be formed of one piece with one another. Furthermore, when the guiding element and the arresting element are formed of one piece, a gap-free connection between the arresting element and the guiding element can be provided.
The spring can act on the guiding element through one or several components or preferably directly. Additional components, structural space and costs can be therefore saved.
In accordance with another embodiment of the present invention, the arresting element can be pressed by the spring against an operational curve, on which the arresting element is always guided with a simple linear contact, and preferably through a linear contact which extends perpendicular to a movement direction of the arresting element.
The arresting element, in the case of the open safety coupling, can be guided along the operational curve in a strike-free manner. Sudden movements of the arresting element, the guiding element and the spring and thereby resulting spring breakage can be avoided, and in particular the settling phenomena of the spring can be reduced.
A hydrodynamic sliding film of lubricant can be provided between the arresting element and the operational curve. For this purpose the arresting element is supported on the operational curve, so that between the curve and the arresting element a diverging gap is formed in a movement direction of the arresting element.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.